Printed circuit boards and other electronic parts generally include electrically conductive patterns or tracks formed on a non-conductive surface of a substrate. The electrically conductive patterns are traditionally formed by selectively applying an etchant to a layer of conductive material applied onto the non-conductive surface of the substrate. Portions of the conductive layer that contact the etchant are removed to reveal the surface of the substrate, and portions of the conductive layer that are not contacted by the etchant remain in the form of the desired conductive pattern. Selective application of the etchant is normally accomplished by placing an etch resistant mask over the conductive layer such that only those portions of the conductive material intended to form the conductive patterns are covered with the etch resistant mask. During etching, revealed portions of the conductive layer are removed, while portions covered with the mask remain. The etch resistant mask may then be removed to reveal a conductive metal pattern.
A conventional method of forming an etch resistant mask is to apply a layer of etch resistant material over the conductive layer. The etch resist material may then be pattern-wise exposed to radiation, such that exposed portions of the mask are less resistant to a developer than unexposed portions. The unexposed portions are then removed by a developer form an etchant resistant mask in a desired pattern. During etching, portions of the conductive layer not covered by the mask are etched away to reveal a non-conductive substrate. However, undeveloped portions of the etch resistant material and the conductive material underneath those portions remain. The unexposed portions of the etch resistant material may then be removed by known stripping processes to reveal a conductive metal pattern on the substrate. One drawback to this method of forming a conductive pattern is that a radiation exposure step, development step and an etching step are required.
An alternative method for forming an etch resistant mask is reported in WO 95/23244. In this reported method, an etch resistant mask may be formed by patternwise applying an etch resistant material via an ink-jet printer. The printed circuit board is then selectively etched to remove portions of the conductive layer not covered by the etch resistant mask. The etch resistant mask may then be removed to expose the conductive metal pattern. Although this method eliminates the radiation exposure step required by conventional mask formation, an etching step must still be performed.
WO 02/47447 reports a method of forming an electronic part in which a non-conductive material is patternwise ink-jet applied to a substrate surface to provide a channel into which a conductive material may then be deposited. The channel is created to prevent the lateral spread of conductive material that may create undesirable short circuits between conductive patterns. Although the reported method eliminates the radiation and etching steps of traditional electronic part formation, a non-conductive material must still be applied to the substrate prior to application of the conductive ink.
It has been recognized that it would be desirable to avoid the radiation, development and/or etching steps by directly patternwise applying a conductive material to a substrate to form an electronic part. However, accomplishing patternwise application of electrically conductive material is problematic for several reasons. First, as noted in WO 02/47447, conventional conductive materials may have a tendency to spread on the substrate surface before solidifying. Second, the high loading of conductive particles generally required to provide patterns with good electrical conduction tends to increase the viscosity of the deposition liquid to a point at which ink-jet application is difficult or impossible. Third, conductive materials that have been ink-jet applied may lack suitable electrical conductivity for certain applications